A computed tomography (CT) scanner includes a rotating portion rotatably supported by a stationary portion. The rotating portion supports an x-ray tube, which emits radiation that traverses an examination region and an object or a subject therein, and a detector array that detects radiation traversing the examination region and generates projection data indicative of the detected radiation. A subject support supports the object or subject in the examination region before, during and/or after scanning, for example, for loading the object or subject, feeding the object or subject into and removing the object or subject from the examination region, and unloading the object or subject. A reconstructor reconstructs the projection data and generates volumetric image data indicative of the portion of the object or subject in the examination region.
The subject support includes a base, which is affixed to the floor of the examination room and is configured to move vertically, under electronic control, with respect to the floor, and a tabletop, which is affixed to the base and is configured to translate horizontally, under electronic control or manually via a user, with respect to the base, in and out of the examination region before, during and/or after scanning. The scanner also includes circuitry to prevent and/or controllably stop electronically controlled vertical and horizontal motion respectively of the base and the tabletop, for example, in response to controlled and uncontrolled removal of power, to prevent a collision, to mitigate a detected collision, or in response to a fault in the subject support drive system. Such circuitry has been configured so that the stopping of the moving subject support complies with certain standards and is comfortable to a patient.
By way of example, IEC 60601 revs 1 and 2 require stopping an electronically controlled moving tabletop in ten millimeters (10 mm) and IEC 60601 rev 3 requires stopping an electronically controlled moving tabletop in twenty-five millimeters (25 mm), both within a half a second (0.5 s) from the time of removal of power and with a one hundred and thirty-five kilogram (135 kg) load, with subsequent placement of the tabletop in a free float state. A conventional tabletop has been configured to translate at speeds up to two hundred millimeters per second (200 mm/s) and satisfy the above-noted IEC requirements by removing power supplied to the tabletop motor and letting the tabletop coast to a stop.
Unfortunately, such braking at higher speeds would add to overall system cost due to the higher peak power requirement and may also introduce discomfort and/or risk to lighter weight patients if the braking current is determined for a heavier load. Furthermore, at higher speeds, if horizontal and vertical collisions or drive chain failures cannot be detected in time, such motion can cause damage to the subject support and/or objects external to the subject support. Furthermore, attaching subject support accessories to the subject support may change allowable vertical and/or horizontal motion of the subject support, which may lead to collisions for a given the collision envelope that otherwise would not occur. Moreover, conventional imaging systems may provide less then desired support and/or mechanisms for securing certain accessories to the subject support.